Pirates in a hijacked ship carrying more than 30 battle tanks were anchored off the coast of Somalia near a notorious pirate den Saturday, and they vowed not to release the ship until a $35 million ransom was paid, Somali and Kenyan officials said.

Meanwhile, a U.S. Navy destroyer, the Howard, was closing in on the hijacked ship.

"We've got a constant stare on it," said Rear Adm. Gregory Smith, a U.S. military spokesman. He would not say how far away the destroyer was but said that the U.S. ship was close enough to maintain visual contact of the hijacked vessel. He also said there were no imminent operations planned against it.

According to Mohamed Osman Aden, a Somali diplomat in Kenya, the Ukrainian-owned vessel was headed to Xarardheere Saturday, on the barren Somali coast. Xarardheere is an isolated fishing village that has thrived on organized crime and has frequently been used as a sanctuary for those who have hijacked ships.

Mohamed said that while the cargo in this case is extremely unusual - 33 Soviet-designed T-72 tanks and a large supply of ammunition and grenade launchers, all intended for the Kenyan military - the tactics were pretty typical.

"These guys just want the money," he said.

He predicted that the pirates would reduce their ransom demand to $1 million to $2 million, though Ukrainian officials have not said whether they will pay any ransom.

In addition to the American destroyer, a Russian frigate, the Dauntless, was on its way.

Diplomats in Kenya said Saturday that military operations involving several countries were being discussed but that the plan was to wait a few days before considering a strike.

The hijacked ship's crew is mostly Ukrainian, and already worried family members have contacted the Ukrainian Foreign Ministry asking what they can do.

The hijacking occurred Thursday evening when pirates in three speedboats attacked the Ukrainian cargo ship Faina, which was in Somali waters about 200 miles from shore, en route to Kenya.

On Friday, Kenyan and Ukrainian officials disclosed that the ship was loaded with 2,320 tons of weapons. Many diplomats in Kenya are concerned that the arms could fall into the hands of insurgents fighting Somalia's transitional government and pitch war-torn Somalia deeper into chaos.

The pirates, however, are not expected to be able to do much with the T-72 tanks because each weighs more than 80,000 pounds. Western diplomats have said that the pirates do not have the special equipment or the skill to get the tanks ashore.

But the tanks - and the jitters they have caused - may be used for leverage to increase the ransom. Andrew Mwangura, program coordinator for the Seafarers' Assistance Program in Kenya, which tracks pirate attacks, said that the pirates had demanded $35 million through intermediaries and that they were trying to contact the ship's owners.

"They even have someone who speaks English," he said.

Piracy in lawless Somalia is a highly organized, lucrative, ransom-driven business. This year has been one of the worst on record, with more than 50 ships attacked, 25 hijacked and about a dozen currently being held by pirates. On Saturday, pirates released two ships they had recently seized, one Japanese and the other Malaysian, Mwangura said.